This invention relates to dynamoelectric machines and in particular to an electronically commutated motor having a rotatable assembly having skewed magnetics for reducing cogging and having a stationary assembly with notched teeth to reduce cogging.
While conventional brush-commutated DC motors may have advantageous characteristics, including convenience of changing operational speeds, there may be disadvantages such as cogging, brush wear, electrical loss, noise and radio frequency interference caused by sparking between the brushes and the segmented commutator, which may limit the applicability of such brush-commutated DC motors in some fields such as the furnace blower control field. Electronically commutated motors, such as brushless DC motors and permanent magnet motors with electronic commutation, have now been developed and generally are believed to have advantageous characteristics over brush commutated DC motors without many of the disadvantages thereof while also having other important advantages.
Various circuit and motor designs have been utilized in the past to develop various types of brushless DC motors, as exemplified in U.S. Pat. No. 4,005,347 issued Jan. 25, 1977, U.S. Pat. No. 4,015,182 issued Mar. 29, 1975, and U.S. Pat. No. 4,449,079 issued May 15, 1984, each of which are incorporated herein by reference. Such brushless DC motors have a stator with a plurality of windings therein, a rotor with a plurality of constant magnetic polar regions providing variable air gap energy, and sensors for sensing the relative position of the rotor polar regions with respect to the stator. Signals developed by the position sensors were processed by circuitry for selectively energizing the windings of the motor.
Further improvements in electronically commutated motor systems can beneficially contribute to more widespread use of such motors in various applications including air handling and pumping systems. Improvements which reduce cogging and which achieve constant torque and speed while maintaining a back electromotive force (EMF) having a waveform with a maximized flat top width would be desirable.